From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4E353C433E0 for ; Wed, 6 Jan 2021 14:47:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id F3EB32311B for ; Wed, 6 Jan 2021 14:47:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727289AbhAFOrE (ORCPT ); Wed, 6 Jan 2021 09:47:04 -0500 Received: from mail.kernel.org ([198.145.29.99]:60708 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726680AbhAFOrC (ORCPT ); Wed, 6 Jan 2021 09:47:02 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 0CA7323100; Wed, 6 Jan 2021 14:46:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1609944382; bh=VDYduDZ2hYzgBR2lAzOGuFpTrOM22sbWMH0q5980R7o=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=bb2QQWnkMIfGcV6jACTTjibZJuLKMNz+CgcJhVbTadUtcbc4pUTIEyNhT7Mi7tm4v LNTxWhcEbl4cPzoicZOdBf6IA5MaomPwPWRBiYdMCHf/Pm0JjABrAPljY9JYG22dNL 181H/DQWYOfWmRX2tvr4kDS9STTX8AYxVWVtbTD2OE6fFf/mAydUUX8W3CAor9ljZg rIlzkEMOgLCxDQ4fZqyxgVx/lBS2PC2+QDxpZZmjb0jM43Vu0kPSQaGQxomSCIrVJb 6DVvlvfaQb2LE9mF1qcm7KEw/Ajeb61kCfyCrbl32vWWBjCcJYzWj+jFobM+J3FISm x0X+YZRpusqUg== Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id B877135225EC; Wed, 6 Jan 2021 06:46:21 -0800 (PST) Date: Wed, 6 Jan 2021 06:46:21 -0800 From: "Paul E. McKenney" To: Peter Zijlstra Cc: tglx@linutronix.de, linux-kernel@vger.kernel.org, valentin.schneider@arm.com, bristot@redhat.com, frederic@kernel.org Subject: Re: lockdep splat in v5.11-rc1 involving console_sem and rq locks Message-ID: <20210106144621.GJ17086@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20210105220115.GA27357@paulmck-ThinkPad-P72> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jan 06, 2021 at 10:52:14AM +0100, Peter Zijlstra wrote: > On Tue, Jan 05, 2021 at 02:01:15PM -0800, Paul E. McKenney wrote: > > Hello! > > > > The RUDE01 rcutorture scenario (and less often, the TASKS01 scenario) > > results in occasional lockdep splats on v5.11-rc1 on x86. This failure > > is probabalistic, sometimes happening as much as 30% of the time, but > > sometimes happening quite a bit less frequently. (And yes, this did > > result in a false bisection. Why do you ask?) The problem seems to > > happen more frequently shortly after boot, so for fastest reproduction > > run lots of 10-minute RUDE01 runs, which did eventually result in a > > good bisection. (Yes, I did hammer the last good commit for awhile.) > > > > The first bad commit is 1cf12e08bc4d ("sched/hotplug: Consolidate task > > migration on CPU unplug"). An example splat is shown below. > > > > Thoughts? > > The splat is because you hit a WARN, we're working on that. Huh. The WARN does not always generate the lockdep complaint. But fair enough. > https://lkml.kernel.org/r/20201226025117.2770-1-jiangshanlai@gmail.com Thomas pointed me at this one a couple of weeks ago. Here is an additional fix for rcutorture: f67e04bb0695 ("torture: Break affinity of kthreads last running on outgoing CPU"). I am still getting WARNs and lockdep splats with both applied. What would break if I made the code dump out a few entries in the runqueue if the warning triggered? Thanx, Paul